This invention relates generally to the fastener drive tool art and more particularly to a fastener drive tool which retains a fastener on the end thereof.
In many fastener applications it is desirable to retain the fastener on the end of the drive tool and to prevent the fastener from wobbling while it is being driven. Retention of a fastener on the end of a drive tool allows the fastener to be driven in an area which might normally be inaccessible and permits single handed use of the drive tool since one hand is not occupied holding and positioning the fastener. In retaining a fastener on a drive tool, an easily releasable securely retaining friction fit is preferred. Prior art fastener retaining drive tools have employed retaining features including magnetic retainers, external fastener retaining fingers as well as spirally formed drive bits.
Each of the aforementioned prior art retaining features has limitations and generally results in a degree of wobble while the fastener is being driven by the drive tool. A common problem encountered by most fastener retaining drive tools is that the variation in tolerances between a drive tool bit portion and a fastener socket deter retention of the fastener on the drive tool.
The type of engagement between the fastener and the driver is very important since prior art fastener drive systems do not provide sufficient retaining forces between the driver and the fastener. For example, many prior art systems have problems with "cam out", which forces the bit portion out of the fastener recess, potentially damaging the surface of the area surrounding the fastener. Cam out occurs when driving torque is applied to the inclined walls in the recesses formed in typical prior art fasteners such as cruciforms or Philips-type fasteners. While in certain situations cam out can be overcome by increasing the end load on the driver to more securely force it into the recess, additional end load will increase the damage caused to the surrounding surface if and when the driver "cams out" of the recess.
With regard to problems with wobbling, prior art fasteners mentioned above wobble while being driven as a result of the insufficient mating between the drive tool and the fastener recess. If a fastener wobbles while being driven the fastener creates an oversized hole which decreases the degree of intimate engagement and hence retaining strength between the fastener and the object in which it is driven. Further, if the fastener is incorrectly driven, the fastener head may protrude above the surrounding surface and joined members may be misaligned.
While some prior art drivers and fasteners have been developed which substantially overcome cam out, these fasteners still may have a degree of wobble about the central axis extending through the fastener and drive tool. In one type of prior art fastener and drive tool, the fastener has a recess formed on a top surface of the head and the driver has a cooperatively mating male protrusion which is formed to engage the recess in the fastener. An example of such a fastener and driver combination is the standard hexalobular TORX fastener and corresponding driver, U.S. Pat. No. 3,584,667. The standard TORX fastener employs a driver bit which has six equidimensioned and equispaced curves lobes which engage in corresponding cross-sectional shaped recesses in the head of the fastener. The sides of the standard TORX fastener are generally parallel to the central axis. Retention of the TORX fastener on the drive tool is at least partly dependent upon the tolerances between the drive tool and the fastener and typically there is a degree of wobble resulting from variations in these tolerances.
The tolerances between the drive tool and fastener, while generally rather precise, may vary. While most fasteners are retainable on the drive tool, if a batch of fasteners are produced at the extreme of the large acceptable tolerance for fasteners and a drive tool is formed at a generally small acceptable tolerance for drive tools the fasteners probably will not be retainable on the drive tool. Further, even with minor, and acceptable, tolerance variations, a degree of wobble is created when the fastener is driven by the drive tool. The problem concerning tolerances is further exacerbated when the drive tool is used for driving a large number of fasteners such that the material on the outside of the drive tool becomes worn. Wear typically reduces the material on the outside surface of the drive tool and therefore increases the disparity between the drive tool and fastener tolerances.
In attempting to overcome some of the aforementioned problems, at least one prior art fastener and drive tool claims to overcome both retention and the wobbling problems. Such a fastener is believed to have been formed with a tool and fastener engagement design similar to the hexalobular design of a standard TORX fastener. However, this prior art device was formed with a slight spiral curve to the lobes on the outside of the drive tool and a corresponding spiral curve to the cooperatively formed mating recess in the fastener. While a fastener might be retainable on a tool using such spirally formed surfaces, it is believed that it is very difficult to remove the drive tool from the fastener once driven. Difficulty in removing the drive tool from the fastener could actually result in loosening the fastener once driven. Further, since this type of fastener and drive tool are specialized, the drive tool only drives specific types of fasteners and cannot be used with other types of standard fasteners.
Therefore, it would be preferable to provide a drive tool which is capable of retaining a fastener thereon and preventing wobble while driving the fastener. Further, it is desirable to provide a drive tool which retains a fastener on the end thereof and reduces wobble and which may be used with standard fasteners.
Further, it is desirable to provide a fastener retaining drive tool which creates substantial fastener retaining forces and which also permits the fastener to be controllably released by complete removal of such forces.
The present invention, as will be detailed more fully hereinafter, overcomes the above-described problems. More specifically, the present invention provides a drive tool which retains a fastener on the end thereof, prevents wobbling of the fastener while it is driven, is generally easily removable from the fastener and may be employed to drive standard non-specialized fasteners.